Axial blower

ABSTRACT

An axial blower includes a rotating blade assembly including a plurality of blades, a motor that rotates the rotating blade assembly to generate an airflow, and a bell mouth that is a frame surrounding the rotating blade assembly from a direction perpendicular to the rotation axis of the rotating blade assembly, wherein the bell mouth has an inlet curved surface on an upstream side of the airflow, the inlet curved surface becomes narrower toward a downstream side of the airflow in the axial direction of the rotation axis, and R 1 /D≤0.05 is satisfied where D represents the outer diameter of the rotating blade assembly, and R 1  represents the radius of curvature of the inlet curved surface.

FIELD

The present invention relates to an axial blower that generates an airflow that flows in the axial direction of a rotation axis.

BACKGROUND

Axial blowers are often installed at places close to living spaces, and there have thus been demands for lowering noise thereof. For achieving lower noise of an axial blower, inclining blades of a rotating blade assembly toward the upstream side of an airflow, and bending outer peripheries of blades of a rotating blade assembly toward the upstream side of an airflow have been proposed.

Bell mouths are formed around rotating blade assemblies of axial blowers, so that air is smoothly sucked into the rotating blade assemblies. The shape of the bell mouths affects the air blowing performance and the noise characteristics of the axial blowers. Thus, as described in Patent Literature 1, there have been attempts to enhance the air blowing performance and the quietness of axial blowers by devising the shapes of bell mouths.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Patent Application Laid-open No. 2002-257096

SUMMARY Technical Problem

The air blowing performance and the noise characteristics of an axial blower are significantly affected not only by the shape of a rotating blade assembly but also the shape of a bell mouth, and the shape of the rotating blade assembly and the shape of the bell mouth are therefore designed to satisfy a required air blowing performance and required noise characteristics. When the rotating blade assembly and the bell mouth are individually designed, however, the shapes thereof may not be necessarily ideal for the air blowing performance and the noise characteristics owing to dimensional constraints.

The present invention has been made in view of the above, and an object thereof is to provide an axial blower with improved air blowing performance and noise characteristics based on the shape of a bell mouth and the shape of a rotating blade assembly.

Solution to Problem

To solve the above problems and achieve the object, an axial blower according to the present invention includes: a rotating blade assembly including a plurality of blades; a motor to rotate the rotating blade assembly to generate an airflow; and a bell mouth being a frame surrounding the rotating blade assembly from a direction perpendicular to a rotation axis of the rotating blade assembly. The bell mouth has an inlet curved surface on an upstream side of the airflow, the inlet curved surface becoming narrower toward a downstream side of the airflow in an axial direction of the rotation axis, and R1/D≤0.05 is satisfied where D represents an outer diameter of the rotating blade assembly, and R1 represents a radius of curvature of the inlet curved surface.

Advantageous Effects of Invention

An axial blower according to the present invention produces effects of improving air blowing performance and noise characteristics based on the shape of a bell mouth and the shape of a rotating blade assembly.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a rotating blade assembly of an axial blower according to an embodiment of the present invention.

FIG. 2 is a drawing illustrating positional relation between a rotating blade assembly and a bell mouth of the axial blower according to the embodiment.

FIG. 3 is a front view of the axial blower according to the embodiment.

FIG. 4 is a cross-sectional view of the axial blower according to the embodiment.

FIG. 5 is a plan view illustrating the shape of a blade of the axial blower according to the embodiment.

FIG. 6 is a cross-sectional view of a blade of the axial blower according to the embodiment.

FIG. 7 is a diagram illustrating the shape of a blade cross section of a blade of the axial blower according to the embodiment and the airflow condition.

FIG. 8 is a diagram illustrating the shape of a blade cross section of a blade of the axial blower according to the embodiment and the airflow condition.

FIG. 9 is a diagram illustrating the shape of a blade cross section of a blade of the axial blower according to the embodiment and the airflow condition.

FIG. 10 is a diagram illustrating the shape of a blade cross section of a blade of the axial blower according to the embodiment and the airflow condition.

FIG. 11 is a graph illustrating the relation between a blade cross-sectional position and radius of curvature of a blade of the axial blower according to the embodiment.

FIG. 12 is a graph illustrating the relation between the ratio of the radius of an inlet curved surface of the bell mouth to the outer diameter of the rotating blade assembly and the air volume at a release point at which the static pressure becomes 0 in the axial blower according to the embodiment.

FIG. 13 is a graph illustrating the relation between the ratio of the radius of the inlet curved surface of the bell mouth to the outer diameter of the rotating blade assembly and the noise level of front noise at the release point in the axial blower according to the embodiment.

FIG. 14 is a graph illustrating the relation between the ratio of the radius of the inlet curved surface of the bell mouth to the outer diameter of the rotating blade assembly and the noise level in the direction inclined 45° at the release point in the axial blower according to the embodiment.

FIG. 15 is a graph illustrating the relation between the ratio of a cut length of the inlet curved surface of the bell mouth to the radius of curvature of the inlet curved surface of the bell mouth and the air volume at the release point in the axial blower according to the embodiment.

FIG. 16 is a graph illustrating the relation between the ratio of the cut length of the inlet curved surface of the bell mouth to the radius of curvature of the inlet curved surface of the bell mouth and the noise level of front noise at the release point in the axial blower according to the embodiment.

FIG. 17 is a graph illustrating the relation between the ratio of the cut length of the inlet curved surface of the bell mouth to the radius of curvature of the inlet curved surface of the bell mouth and the noise level in the direction inclined 45° at the release point in the axial blower according to the embodiment.

FIG. 18 is a graph illustrating the relation between air volume and static pressure in the axial blower according to the embodiment depending on the ratio of the radius of curvature of the inlet curved surface of the bell mouth to the outer diameter of the rotating blade assembly.

FIG. 19 is a graph illustrating the relation between air volume and the noise level of front noise in the axial blower according to the embodiment depending on the ratio of the radius of curvature of the inlet curved surface of the bell mouth to the outer diameter of the rotating blade assembly.

FIG. 20 is a graph illustrating the relation between air volume and the noise level of diagonal noise in the axial blower according to the embodiment depending on the ratio of the radius of curvature of the inlet curved surface of the bell mouth to the outer diameter of the rotating blade assembly.

FIG. 21 is a graph illustrating the relation between air volume and static pressure in the axial blower according to the embodiment depending on the ratio of the cut length of the inlet curved surface of the bell mouth to the radius of curvature of the inlet curved surface of the bell mouth.

FIG. 22 is a graph illustrating the relation between air volume and the noise level of front noise in the axial blower according to the embodiment depending on the ratio of the cut length of the inlet curved surface of the bell mouth to the radius of curvature of the inlet curved surface of the bell mouth.

FIG. 23 is a graph illustrating the relation between air volume and the noise level of diagonal noise in the axial blower according to the embodiment depending on the ratio of the cut length of the inlet curved surface of the bell mouth to the radius of curvature of the inlet curved surface of the bell mouth.

FIG. 24 is a graph illustrating a difference in the relation between air volume and static pressure depending on the difference in the radius of curvature of the inlet curved surface of the bell mouth in the axial blower according to the embodiment.

FIG. 25 is a graph illustrating a difference in the relation between air volume and the noise level of front noise depending on the difference in the radius of curvature of the inlet curved surface of the bell mouth in the axial blower according to the embodiment.

FIG. 26 is a graph illustrating a difference in the relation between air volume and the noise level of diagonal noise depending on the difference in the radius of curvature of the inlet curved surface of the bell mouth in the axial blower according to the embodiment.

DESCRIPTION OF EMBODIMENTS

An axial blower according to an embodiment of the present invention will be described in detail below with reference to the drawings. Note that the present invention is not limited to the embodiment.

Embodiment

FIG. 1 is a perspective view of a rotating blade assembly of an axial blower according to an embodiment of the present invention. FIG. 2 is a drawing illustrating a positional relation between a rotating blade assembly and a bell mouth of the axial blower according to the embodiment. The rotating blade assembly 1 according to the embodiment includes a columnar boss 2, and three blades 1 a attached to the boss 2. Although the shape of one of the three blades 1 a will be mainly described in the description below, the three blades 1 a have the same shape.

A blade 1 a has a three-dimensional shape. The blade 1 a is radially attached to the outer circumference of the boss 2. The boss 2 is driven to rotate about a rotation axis AX by a motor 3. The blade 1 a rotates with the boss 2 in the direction of an arrow S, to generate an airflow flowing in the direction of an arrow A.

The rotating blade assembly 1 is positioned at the center of a blower main unit 6 that includes the bell mouth 5. The blower main unit 6 is a frame having a square outer shape in front view. The motor 3 is positioned downstream of the bell mouth 5 in the airflow direction. Alternatively, the motor 3 may be positioned upstream of the bell mouth 5 in the airflow direction.

FIG. 3 is a front view of the axial blower according to the embodiment. FIG. 4 is a cross-sectional view of the axial blower according to the embodiment. In FIG. 4, the shape of the blade 1 a on a meridian plane is illustrated. The bell mouth 5 includes an inlet curved surface 51, a straight portion 53, and an outlet curved surface 52. The inlet curved surface 51 is located upstream of the airflow, and the flow passage becomes narrower toward the downstream side of the airflow in the axial direction of the rotation axis AX. The outlet curved surface 52 is located downstream of the airflow, and the flow passage becomes wider toward the downstream side of the airflow in the axial direction of the rotation axis AX. Typically, the inlet curved surface 51 of the bell mouth 5 has a radius of curvature R1 larger than the radius of curvature R2 of the outlet curved surface 52 thereof.

When the length of a side of the outer shape of the blower main unit 6 in front view is represented by L, the outer diameter of the rotating blade assembly 1 is represented by D, and the outer diameter of the inlet curved surface 51 of the bell mouth 5 is represented by DR1, the axial blower 10 is designed to satisfy DR1<L in view of easiness of installation and manufacturing cost. The inlet curved surface 51 is formed to be as large as possible within the length L of one side of the outer shape of the blower main unit 6 in front view, so that the airflow is smoothly guided into the rotating blade assembly 1.

The rotating blade assembly 1 of the axial blower 10 according to the embodiment has an outer diameter D of 260 mm. An outer trailing edge I of the rotating blade assembly 1 is located near the boundary between the straight portion 53 and the outlet curved surface 52 of the bell mouth 5. In addition, a blade leading edge 1 b and a blade outer edge 1 d of the rotating blade assembly 1 project toward the upstream side of the airflow relative to the inlet curved surface 51 of the bell mouth 5.

Because the blade leading edge 1 b and the blade outer edge 1 d of the rotating blade assembly 1 project toward the upstream side of the airflow relative to the inlet curved surface 51 of the bell mouth 5, air flows into the rotating blade assembly 1 not only via the blade leading edge 1 b but also via the blade outer edge 1 d. This increases the cross-sectional area of the flow passage of air flowing into the rotating blade assembly 1, and thus lowers the velocity of the airflow into the rotating blade assembly 1. The decrease in the velocity of the airflow reduces turbulence of the airflow and achieves lower noise.

The straight portion 53 prevents air from flowing backward when static pressure is applied.

The outlet curved surface 52 allows a flow in the centrifugal direction included in the airflow flowing out from the rotating blade assembly 1 to smoothly flow out of the rotating blade assembly 1. In addition, the outlet curved surface 52 also serves as a diffuser that increases the static pressure.

In the axial blower 10 according to the embodiment, the outer diameter D of the rotating blade assembly 1 and the radius of curvature R1 of the inlet curved surface 51 of the bell mouth 5 satisfy the following relation: R1/D≤0.05. In addition, when a difference between the outer diameter DR1′ of the inlet curved surface 51 of the bell mouth 5 when the inlet curved surface 51 is extended so that a tangential line TL at an upstream end 51 a of the inlet curved surface 51 of the bell mouth 5 is perpendicular to the rotation axis AX and the outer diameter DR1 of the inlet curved surface 51 of the bell mouth 5 is represented by R1′, the following relation is satisfied: 0<R1′/R1≤0.505.

The inlet curved surface 51 of the bell mouth 5 of the axial blower 10 according to the embodiment can be assumed to have such a shape that a part corresponding to a length R1′ is removed from the outer circumference of the inlet curved surface 51′ having the outer diameter DR1′, and to have the outer diameter DR1. In other words, in the axial blower 10 according to the embodiment, it can be assumed that the part having the length R1′ is removed from the outer circumference of the inlet curved surface 51′ having the outer diameter DR1′, so that the inlet curved surface 51 of the bell mouth 5 has the outer diameter DR1. Hereinafter, the part assumed to be removed from the inlet curved surface 51′ having the outer diameter DR1′ will be referred to as a cut part. In addition, the length of the cut part will be referred to as a cut length. Thus, in the embodiment, the cut length is R1′.

When the cut part includes a portion ΔL sticking out from one side of the outer shape of the blower main unit 6 in front view, the outer diameter DR1 of the inlet curved surface 51 of the bell mouth 5 is smaller than the length L of one side of the blower main unit 6. When 0<R1′/R1≤0.505 is satisfied as described above, the radius of curvature R1 of the inlet curved surface 51 of the bell mouth 5 is increased, and the bell mouth 5 can be made smaller than the outer shape of the blower main unit 6 in front view.

FIG. 5 is a plan view illustrating the shape of a blade of the axial blower according to the embodiment. FIG. 6 is a cross-sectional view of a blade of the axial blower according to the embodiment. FIG. 6 illustrates a blade cross section of a blade 1 a at a plane along a plane including the rotation axis AX and a blade inner edge 1 e. The blade 1 a has an inflection point IP between the outer side and the inner side at the blade cross section including the rotation axis AX and the blade inner edge 1 e. The blade 1 a has a blade cross section convex to the upstream side of the airflow on the inner side closer to the boss 2 with respect to the inflection point IP, and has a blade cross section convex to the downstream side of the airflow on the outer side farther from the boss 2 with respect to the inflection point IP. The blade 1 a has a curvature R1 b at the blade cross section on the inner side with respect to the inflection point IP. The blade 1 a has a curvature R2 b at the blade cross section on the outer side with respect to the inflection point IP. The radii of curvature R1 b and R2 b of the blade 1 a change continuously from the blade leading edge 1 b to a blade tailing edge 1 c.

FIGS. 7, 8, 9, and 10 are diagrams illustrating the shapes of blade cross sections of a blade of the axial blower according to the embodiment and the airflow condition. FIG. 7 illustrates the shape of a blade cross section at a plane along the radial direction including the rotation axis AX at a blade cross-sectional position O-D1 in FIG. 5. FIG. 8 illustrates the shape of a blade cross section at a plane along the radial direction including the rotation axis AX at a blade cross-sectional position O-D2 in FIG. 5. FIG. 9 illustrates the shape of a blade cross section at a plane along the radial direction including the rotation axis AX at a blade cross-sectional position O-D3 in FIG. 5. FIG. 10 illustrates the shape of a blade cross section at a plane along the radial direction including the rotation axis AX at a blade cross-sectional position O-D4 in FIG. 5. The blade 1 a is inclined at θ(O-D1) toward the upstream side of the airflow at the blade cross-sectional position O-D1, but the inclination angle θ(O-D2) at the blade cross-sectional position O-D2, the inclination angle θ(O-D3) at the blade cross-sectional position O-D3, and the inclination angle θ(O-D4) at the blade cross-sectional position O-D4 change in such a manner that the blade 1 a is more inclined toward the downstream side of the airflow as the position is closer to the blade tailing edge 1 c. Although a lateral flow 9 parallel to the blade cross section is present near the blade leading edge 1 b of the rotating blade assembly 1, a side face of the rotating blade assembly 1 projects toward the upstream side of the airflow relative to the bell mouth 5, which enables the lateral flow 9 to be drawn into the rotating blade assembly 1. The inclination of the blade cross section changes in such a manner that the entire blade cross section is more inclined toward the downstream side of the airflow as the position is closer to the blade tailing edge 1 c of the rotating blade assembly 1. The pressure of the airflow is increased by controlling a radial flow 11, which tends to flow in the centrifugal direction as the pressure increases, so as not to leak out of the rotating blade assembly 1.

As illustrated in FIGS. 7 and 8, the blade 1 a has a blade cross section in which the inner side thereof is away from the boss 2 at a position near the front in the rotating direction.

When the rotating blade assembly 1 rotates, a blade tip vortex 7 is generated by a pressure difference between the pressure surface and the negative pressure surface of the blade 1 a. When the blade tip vortex 7 interferes with: the negative pressure surface of the blade 1 a; another adjacent blade 1 a; or the bell mouth 5, the noise characteristics of the axial blower 10 lower. Because the blade 1 a has an S-shaped blade cross section convex to the upstream side of the airflow on the inner side and convex to the downstream side of the airflow on the outer side, generation of the blade tip vortex 7 is reduced, and the flow with an increased pressure is prevented from leaking out of the rotating blade assembly 1.

FIG. 11 is a graph illustrating the relation between a blade cross-sectional position and radius of curvature of a blade of the axial blower according to the embodiment. The radius of curvature R1 b on the inner side of the blade 1 a gradually decreases from the blade leading edge 1 b toward the blade tailing edge 1 c. In contrast, the radius of curvature R2 b on the outer side of the blade 1 a gradually decreases from the blade leading edge 1 b to the blade cross-sectional position O-D3, and gradually increases from the blade cross-sectional position O-D3 to the blade tailing edge 1 c.

FIG. 12 is a graph illustrating the relation between the ratio of the radius of the inlet curved surface of the bell mouth to the outer diameter of the rotating blade assembly and the air volume at a release point at which the static pressure 0 in the axial blower according to the embodiment. Note that, in FIG. 12, the air volume is normalized so that the air volume at the release point is 100%. As illustrated in FIG. 12, the air volume tends to increase as the ratio R1/D of the radius of curvature R1 of the inlet curved surface 51 of the bell mouth 5 to the outer diameter D of the rotating blade assembly 1 is larger.

FIG. 13 is a graph illustrating the relation between the ratio of the radius of the inlet curved surface of the bell mouth to the outer diameter of the rotating blade assembly and the noise level of front noise at the release point in the axial blower according to the embodiment. Note that, in FIG. 13, the noise level is normalized so that the noise level at the release point is 0 dB. The noise level of the front noise is smaller as the ratio R1/D of the radius of curvature R1 of the inlet curved surface 51 of the bell mouth 5 to the outer diameter D of the rotating blade assembly 1, but unlike the air volume, the noise level of the front noise hardly changes with the increase in R1/D after the noise level reaches a certain small level.

FIG. 14 is a graph illustrating the relation between the ratio of the radius of the inlet curved surface of the bell mouth to the outer diameter of the rotating blade assembly and the noise level in the direction inclined 45° at the release point in the axial blower according to the embodiment. Note that, in FIG. 14, the noise level is normalized so that the noise level at the release point is 0 dB. In a manner similar to the noise level of front noise, the noise level becomes smaller as R1/D becomes larger. The noise level in the direction inclined 45° is, however, different from the noise level of front noise in that the noise level in the direction inclined 45° at the release point does not stop decreasing from a certain level.

It can be seen in FIGS. 12, 13, and 14 that the air volume and the noise characteristics improve as the ratio R1/D of the radius of curvature R1 of the inlet curved surface 51 of the bell mouth 5 to the outer diameter D of the rotating blade assembly 1 becomes larger.

FIG. 15 is a graph illustrating the relation between the ratio of the cut length of the inlet curved surface of the bell mouth to the radius of curvature of the inlet curved surface of the bell mouth and the air volume at the release point in the axial blower according to the embodiment. Note that, in FIG. 15, the air volume is normalized so that the air volume at the release point is 100%. As illustrated in FIG. 15, when the ratio R1′/R1 of the cut length R1′ of the inlet curved surface 51 of the bell mouth 5 to the radius of curvature R1 of the inlet curved surface 51 of the bell mouth 5 is equal to or smaller than 0.45, the air volume is not dependent on R1′/R1. When R1′/R1 exceeds 0.45, the air volume decreases sharply.

FIG. 16 is a graph illustrating the relation between the ratio of the cut length of the inlet curved surface of the bell mouth to the radius of curvature of the inlet curved surface of the bell mouth and the noise level of front noise at the release point in the axial blower according to the embodiment. Note that, in FIG. 16, the noise level is normalized so that the noise level at the release point is 0 dB. As illustrated in FIG. 16, when R1′/R1 is equal to or smaller than 0.45, the noise level of the front noise lowers. When R1′/R1 exceeds 0.5, however, the noise level of the front noise becomes larger than that at R1′/R1=0.

FIG. 17 is a graph illustrating the relation between the ratio of the cut length of the inlet curved surface of the bell mouth to the radius of curvature of the inlet curved surface of the bell mouth and the noise level in the direction inclined 45° at the release point in the axial blower according to the embodiment. Note that, in FIG. 17, the noise level is normalized so that the noise level at the release point is 0 dB. In a manner similar to the noise level of the front noise, when R1′/R1 is equal to or smaller than 0.45, the noise level of the noise lowers. When R1′/R1 exceeds 0.5, however, the noise level of the noise becomes larger than that at R1′/R1=0.

It can be seen in FIGS. 15, 16, and 17 that a range in which the relative change rates are suitable is present between the ratio R1′/R1 of the cut length R1′ of the inlet curved surface 51 of the bell mouth 5 to the radius of curvature R1 of the inlet curved surface 51 of the bell mouth 5 and the air volume or the noise level of the noise. In a range of 0<R1′/R1≤0.505, the change in noise at R1′/R1=0 corresponding to the bell mouth with the inlet curved surface having the outer diameter DR1′ before the cut part is removed is within +0.5 (dB), which achieves lower noise.

FIG. 18 is a graph illustrating the relation between air volume and static pressure in the axial blower according to the embodiment depending on the ratio of the radius of curvature of the inlet curved surface of the bell mouth to the outer diameter of the rotating blade assembly. FIG. 19 is a graph illustrating the relation between air volume and the noise level of front noise in the axial blower according to the embodiment depending on the ratio of the radius of curvature of the inlet curved surface of the bell mouth to the outer diameter of the rotating blade assembly. FIG. 20 is a graph illustrating the relation between air volume and the noise level of diagonal noise in the axial blower according to the embodiment depending on the ratio of the radius of curvature of the inlet curved surface of the bell mouth to the outer diameter of the rotating blade assembly. As illustrated in FIGS. 18, 19, and 20, as the ratio R1/D of the radius of curvature R1 of the inlet curved surface 51 of the bell mouth 5 to the outer diameter D of the rotating blade assembly 1 becomes larger, the static pressure becomes higher and the noise level of the noise becomes lower not only as the characteristics at the release point at which the static pressure is 0 but also in another practical air volume range.

FIG. 21 is a graph illustrating the relation between air volume and static pressure in the axial blower according to the embodiment depending on the ratio of the cut length of the inlet curved surface of the bell mouth to the radius of curvature of the inlet curved surface of the bell mouth. FIG. 22 is a graph illustrating the relation between air volume and the noise level of front noise in the axial blower according to the embodiment depending on the ratio of the cut length of the inlet curved surface of the bell mouth to the radius of curvature of the inlet curved surface of the bell mouth. FIG. 23 is a graph illustrating the relation between air volume and the noise level of diagonal noise in the axial blower according to the embodiment depending on the ratio of the cut length of the inlet curved surface of the bell mouth to the radius of curvature of the inlet curved surface of the bell mouth. As illustrated in FIGS. 21, 22, and 23, at R1′/R1=0.447, which is in a suitable range of R1′/R1, the static pressure hardly changes from the state at R1′/R1=0 and the noise improved only as the characteristics at the release point at which the static pressure is 0 but also in another practical air volume range. In addition, at R1′/R1=0.733, which is out of the suitable range of R1′/R1, the static pressure and the noise characteristics lower not only as the characteristics at the release point but also in another practical air volume range.

FIG. 24 is a graph illustrating a difference in the relation between air volume and static pressure depending on the difference in the radius of curvature of the inlet curved surface of the bell mouth in the axial blower according to the embodiment. FIG. 25 is a graph illustrating a difference in the relation between air volume and the noise level of front noise depending on the difference in the radius of curvature of the inlet curved surface of the bell mouth in the axial blower according to the embodiment. FIG. 26 is a graph illustrating a difference in the relation between air volume and the noise level of diagonal noise depending on the difference in the radius of curvature of the inlet curved surface of the bell mouth in the axial blower according to the embodiment. R1 ₁>R1 ₂ is satisfied. A graph of R1 ₂ is R1′/R1 ₁=0.333. A graph of R1 ₂ is R1′/R1 ₂=0. As illustrated in FIGS. 24, 25, and 26, as the radius of curvature of the inlet curved surface 51 of the bell mouth 5 is larger, the air volume, the static pressure, and the noise characteristics are improved.

In the axial blower 10 according to the embodiment, the ratio of the radius of curvature R1 of the inlet curved surface 51 of the bell mouth 5 to the outer diameter D of the rotating blade assembly 1 satisfies R1/D≤0.05, which controls increase of noise by turbulence of the airflow generated by the inlet curved surface 51 of the bell mouth 5 and sucked into rotating blade assembly 1. In addition, the outer diameter of the inlet curved surface 51 of the bell mouth 5 is equal to or smaller than the length of a side of the blower main unit 6, which prevents the equipment size from increasing. In addition, because the outer diameter of the inlet curved surface 51 of the bell mouth 5 is equal to or smaller than the length of a side of the blower main unit 6, the need for mounting a bell mouth 5 that is a component separate from a blower main unit 6 onto the blower main unit 6 is eliminated, and an increase in man-hours is thus prevented.

The configurations presented in the embodiment above are examples of the present invention, and can be combined with other known technologies or can be partly omitted or modified without departing from the scope of the present invention.

REFERENCE SIGNS LIST

1 rotating blade assembly; 1 a blade; 1 b blade leading edge; 1 c blade tailing edge; 1 d blade outer edge; 1 e blade inner edge; 2 boss; 3 motor; 5 bell mouth; 6 blower main unit; 7 blade tip vortex; 9 lateral flow; 10 axial blower; 51, 51′ inlet curved surface; 51 a upstream end; 52 outlet curved surface. 

1. An axial blower comprising: a rotating blade assembly including a plurality of blades; a motor to rotate the rotating blade assembly to generate an airflow; and a bell mouth being a frame surrounding the rotating blade assembly from a direction perpendicular to a rotation axis of the rotating blade assembly, wherein the bell mouth has an inlet curved surface on an upstream side of the airflow, the inlet curved surface becoming narrower toward a downstream side of the airflow in an axial direction of the rotation axis, and 0<R1′/R1≤0.505 is satisfied where R1 represents a radius of curvature of the inlet curved surface and R1′ represents a difference between an outer diameter of the inlet curved surface and a length obtained by doubling a distance between a position at which a tangential line at an upstream end of the inlet curved surface is perpendicular to the rotation axis and to which the inlet curved surface is extended and the rotation axis.
 2. The axial blower according to claim 1, wherein R1/D≤0.05 is satisfied where D represents an outer diameter of the rotating blade assembly.
 3. The axial blower according to claim 1, wherein a blade cross section of each blade at a plane along a radial direction including the rotation axis is inclined toward an upstream side of the airflow at a blade leading edge located at a front position in a rotating direction, and an inclination angle continuously changes in such a manner that the blade cross section is more inclined toward a downstream side of the airflow as the blade is closer to a blade tailing edge located at a back position in the rotating direction.
 4. The axial blower according to claim 1, wherein each blade has an inflection point located between an outer side and an inner side, the inflection point being a point at which a direction to which a blade cross section is convex changes, and the blade cross section of the blade is convex to an upstream side of the airflow on an inner side of the inflection point, and convex to a downstream side of the airflow on an outer side of the inflection point.
 5. The axial blower according to claim 4, wherein a radius of curvature of the blade on the outer side of the inflection point gradually decreases from a blade leading edge toward a blade tailing edge, reaches a minimum value, and then gradually increases, and a radius of curvature of the blade on the inner side of the inflection point gradually decreases from the blade leading edge toward the blade tailing edge.
 6. The axial blower according to claim 2, wherein a blade cross section of each blade at a plane along a radial direction including the rotation axis is inclined toward an upstream side of the airflow at a blade leading edge located at a front position in a rotating direction, and an inclination angle continuously changes in such a manner that the blade cross section is more inclined toward a downstream side of the airflow as the blade is closer to a blade tailing edge located at a back position in the rotating direction.
 7. The axial blower according to claim 2, wherein each blade has an inflection point located between an outer side and an inner side, the inflection point being a point at which a direction to which a blade cross section is convex changes, and the blade cross section of the blade is convex to an upstream side of the airflow on an inner side of the inflection point, and convex to a downstream side of the airflow on an outer side of the inflection point.
 8. The axial blower according to claim 3, wherein each blade has an inflection point located between an outer side and an inner side, the inflection point being a point at which a direction to which a blade cross section is convex changes, and the blade cross section of the blade is convex to an upstream side of the airflow on an inner side of the inflection point, and convex to a downstream side of the airflow on an outer side of the inflection point.
 9. The axial blower according to claim 6, wherein each blade has an inflection point located between an outer side and an inner side, the inflection point being a point at which a direction to which a blade cross section is convex changes, and the blade cross section of the blade is convex to an upstream side of the airflow on an inner side of the inflection point, and convex to a downstream side of the airflow on an outer side of the inflection point.
 10. The axial blower according to claim 7, wherein a radius of curvature of the blade on the outer side of the inflection point gradually decreases from a blade leading edge toward a blade tailing edge, reaches a minimum value, and then gradually increases, and a radius of curvature of the blade on the inner side of the inflection point gradually decreases from the blade leading edge toward the blade tailing edge.
 11. The axial blower according to claim 8, wherein a radius of curvature of the blade on the outer side of the inflection point gradually decreases from a blade leading edge toward a blade tailing edge, reaches a minimum value, and then gradually increases, and a radius of curvature of the blade on the inner side of the inflection point gradually decreases from the blade leading edge toward the blade tailing edge.
 12. The axial blower according to claim 9, wherein a radius of curvature of the blade on the outer side of the inflection point gradually decreases from a blade leading edge toward a blade tailing edge, reaches a minimum value, and then gradually increases, and a radius of curvature of the blade on the inner side of the inflection point gradually decreases from the blade leading edge toward the blade tailing edge. 